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Particles and interactions

Particles and interactions

Promethean Particles spins out continuous process for making nanoparticles

12 Apr 2021 Hamish Johnston
Taken from the 2021 Physics World Nanotechnology Briefing. You can enjoy the full issue via the Physics World app.

Chemical engineer Ed Lester developed a continuous production method for making nanoparticles at the University of Nottingham and founded the company Promethean Particles to commercialize the process. He talks to Physics World’s Hamish Johnston about the challenges of making nanoparticles and of creating a university spin-out

Ed Lester
Ed Lester The University of Nottingham chemist founded Promethean Particles in 2007. (Courtesy: Ed Lester)

Promethean Particles produces nanoparticles using a technique called hydrothermal synthesis; how does this process work?

Hydrothermal just means hot water. If you ever made a crystal garden when you were younger, you know that it involves dissolving large amounts of coloured metal salts in a small jar of water. What this does is create a super-saturated solution where the metal ions are ready to effectively “crash out” at the first opportunity. Put a piece of string into this solution and impressive-looking crystals grow onto the string over the next few days or weeks.

Hydrothermal synthesis has been used for hundreds of years to make large crystals (on long timescales) using a very similar process but in large batch autoclaves. In contrast, our crystallization process takes seconds because we are only growing nanocrystals, which are very small clusters of atoms, maybe 100 to 10,000 atoms in size. The nucleation of these particles is instantaneous and occurs in a continuous flow process. This flow process is designed to create a super-saturated solution just for the briefest moment, allowing nanoparticles to form.

How did you develop and commercialize the process?

The original idea for our continuous process came from Japan in the early 1990s, when a very well-known academic called Tadafumi Adschiri described a continuous process using two flows (a very hot flow and a cold flow containing the dissolved metal salts) introduced together in a high pressure T reactor arrangement. At first, we struggled to make nanoparticles in a way that avoided blockages. It took a few years to solve this problem because it was tricky to understand what was happening inside our steel reactor during the high-temperature, high-pressure process.

Once we perfected the process and reactor design, we filed a patent and started generating interest from companies that might want to take it forward. Eventually we took the step to commercialize the technology ourselves and formed Promethean Particles at the end of 2007. The route to commercialization is always an interesting one and the choice of whether to license intellectual property or create a spin-out company is one that academics with good ideas must wrestle with.

The choice of whether to license intellectual property or create a spin-out company is one that academics with good ideas must wrestle with

Did you get guidance from the University of Nottingham when making that decision?

Like most universities, Nottingham has a tech transfer office, and we discussed the possibility of a spin-out with them. We had a market survey commissioned to try to understand the potential marketplace for our products. The results were overwhelmingly positive, and so this gave us the initial confidence that there was a market for this technology.

In particular we discovered that industrial users of nanomaterials were frustrated with the quality of the nanoparticles they were buying and the lack of available industrial scale for other nanoparticles they would otherwise be interested in. One of the key things we offer our customers is the ability to enable them to achieve production scale. It was clear that we could meet their needs in different market sectors from coatings to medical applications, but the technology needed developing and scaling up to meet industrial demand. This positioning was key to our decision to spin out the technology rather than to license it.

Promethean Particles opened a manufacturing facility in Nottingham in 2016. What type of nanoparticles do you make there and what are they used for?

The first products that we made were ceramics – metal oxides that can be used in reflective coatings, high-temperature materials, catalysts or as strengthening materials for fabrics. Today, we can make materials in eight different materials classes including metals, metal oxides and metal-organic frameworks. Furthermore, within some of those classes, (e.g. doped metal oxides) there is a virtually limitless combination of materials that we can produce. These can be used in everything from batteries to anti viral coatings.

We produce both standardized and bespoke materials. We work closely with our customers to understand their needs and take them through our new product development process that first designs the nanomaterial solution, then develops it so it can be scaled, before delivering them the products that they are looking for.

We can make materials in eight different materials classes including metals, metal oxides and metal-organic frameworks

Can you give a flavour of some of the products you are currently working on?

We are working in several different market sectors and we have a few products that are either in or close to market.

We are working on a product that stops ice from building up on aeroplanes. Currently, de-icing is an expensive, time-consuming process that can lead to flight delays. It is done by spraying chemicals on aircraft, which removes ice and creates a temporary coating that prevents ice from forming – but nanoparticles could offer a better, more sustainable route to keeping the outside of the plane ice free. Nanomaterials are already used in exterior coatings to help aeroplanes fly more efficiently. By altering the morphology of these particles and their surface chemistry, we can stop water molecules building up and prevent the formation of ice. Essentially, this is the creation of a textured super-hydrophobic coating, which is also how self-cleaning glass works.

Because of the COVID-19 crisis, there has been great interest in the antiviral and antimicrobial additives that we can produce. We have been developing copper and silver nanoparticle-based inks for printing circuit boards, but it turns out that these metallic nanoparticles are also very good at killing the COVID-19 virus. We have other healthcare/PPE applications that are currently undergoing testing. Healthcare has become a much bigger thing for us in the past year.

We also get a lot of interest in our metal-organic frameworks (MOFs), which are porous materials that have an extremely high surface area. Indeed, a sample of MOFs powder that you can hold in your hand has the same surface area as an office block. This property means these MOFs can be used for gas storage, gas capture or chemical filtration.

We also make a dispersion that can be used as a thermal fluid to improve the efficiency of heating and cooling systems including air conditioning units. Reducing energy consumption is a key sustainability goal. More efficient heating and cooling systems would make a significant difference to global energy demand.

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